A radio frame in a Long Term Evolution (LTE) system and an enhanced LTE (LTE-A, LTE-Advance) system may include a frame structure in a Frequency Division Duplex (FDD) mode and a Time Division Duplex (TDD) mode. With a frame structure in an FDD mode is as shown in FIG. 1, a radio frame of 10 milliseconds (ms) consists of ten subframes numbered as subframe 0-9 respectively, each with a length of 1 ms; a subframe consists of two slots each with a length of 0.5 ms. With a frame structure in a TDD mode as shown in FIG. 2, a radio frame of 10 ms consists of two half frames each with a length of 5 ms; a half frame includes 5 subframes each with a length of 1 ms. In both frame structures, with a Normal Cyclic Prefix (CP), a slot contains 7 symbols each with a length of 66.7 microseconds (us). A Cyclic Prefix (CP) of a first symbol thereof has a length of 5.21 us. A CP of each of the other 6 symbols has a length of 4.69 us. In case of an Extended CP, a slot contains 6 symbols, each with a CP of a length of 16.67 us.
An LTE system corresponds to Release 8 (R8). An LTE-A system corresponds to Release 10 (R10). In both R8 and R10, a Physical Downlink Control Channel (PDCCH) is used for transmitting Downlink Control Information (DCI). In a subframe, a PDCCH is in general configured in the first Orthogonal Frequency Division Multiplexing (OFDM) symbols. In general the first N OFDM symbols may be referred to as a control channel area. In general, a Physical Downlink Shared Channel (PDSCH) is right next to the control channel area; transmitted data occupy physical resources in units of Physical Resource Block (PRB) pairs.
A DCI format may include: a DCI format 0, a DCI format 1, a DCI format 1A, a DCI format 1B, a DCI format 1C, a DCI format 1D, a DCI format 2, a DCI format 2A, a DCI format 2B, a DCI format 2C, a DCI format 3, a DCI format 3A, and a DCI format 4.
The DCI format 0 and the DCI format 4 may be configured for Physical Uplink Shared Channel (PUSCH) scheduling. The DCI format 1, the DCI format 1A, the DCI format 1B, the DCI format 1C, and the DCI format 1D may be configured for indicating a mode in PDSCH codeword scheduling. The DCI format 2, the DCI format 2A, the DCI format 2B, and the DCI format 2C may be configured for indicating a mode in Space Division Multiplexing. The DCI format 3 and the DCI format 3A may be configured for indicating a mode in Physical Uplink Control Channel (PUCCH) and PUSCH power control commands.
Physical resources for PDCCH transmission are managed in units of Control Channel Elements (CCE). A CCE consists of 9 Resource Element Groups (REG), namely, 36 Resource Elements (RE). A PDCCH may occupy 1, 2, 4, or 8 CCEs. A PDCCH occupying 1, 2, 4, or 8 CCEs may adopt tree-like aggregration. Namely, a PDCCH occupying 1 CCE may occupy any CCE; a PDCCH occupying 2 CCEs may perform CCE occupation starting from an even CCE position; a PDCCH occupying 4 CCEs may perform CCE occupation starting from a CCE position corresponding to multiples of 4; a PDCCH occupying 8 CCEs may perform CCE occupation starting from a CCE position corresponding to multiples of 8.
Defined for each aggregration level is a search space, including a common search space and a User Equipment (UE) specific (UE-Specific) search space. A common search space may bear common information on a System Information Block (SIB), Random Access Response (RAR) and Paging. A UE-Specific search space may bear information on uplink and downlink scheduling authorization for a UE. In receiving DCI, a UE should detect common search spaces of aggregration levels 4 and 8, and UE-Specific search spaces of aggregration levels 1, 2, 4, and 8. A common search space and a UE-Specific search space may overlap. A specific number of detections and a corresponding search space is as shown in Table 1.
TABLE 1aggregrationsearch spacecandidatetypelevelsizesetuser-specific166search space21264828162common4164search space8162
In a release after R10, in order to increase control channel transmission capacity and support more user control signaling, a new control channel area, referred to as an enhanced PDCCH (ePDCCH), is set, as shown in FIG. 3, with a bandwidth BW, a hatched PDCCH portion, an ePDCCH portion marked with vertical lines, and a meshed PDSCH portion. An ePDCCH occupies resources formerly occupied by a PDSCH.
Research is to be done on designing a common search space in an ePDCCH. At present, common information may be transmitted using a common search space of a PDCCH area. However, no solution exists for New Carrier Type (NCT) independent operation or for access of a large-bandwidth system by a Low Cost UE. In either case, common information may not be transmitted using a common search space of a PDCCH area, and no solution for interference among common search spaces in a heterogeneous network is available.